1. Field of the Invention
The present invention relates to a sealed lead-acid battery having a good discharge characteristic, a good gas recombination performance and a long life expectency, as well as a sealed lead-acid battery which is unlikely to leak its electrolyte regardless of its orientation. The invention also relates to a process for producing such a sealed lead-acid battery.
2. Description of the Prior Art
A lead-acid battery can be sealed by utilizing a so-called "oxygen cycle" wherein the oxygen gas generated from the positive plates at the end of charge is recombined by the negative plates. In order to promote the movement of the oxygen gas generated by the positive plates to the negative plates and the velocity of the combination with the oxygen gas of the negative plates or, in other words, to increase the gas recombination rate, the amount of the electrolyte in the plate group must be kept as small as possible. Also, in order to prevent the sulfuric acid electrolyte from leaking out of the battery and to increase the leakproofness of the battery, it is not desirable that the unfixed free sulfuric acid electrolyte be present in the battery and therefore it is necessary that the sulfuric acid electrolyte be fixed only in the pores in the positive and negative plates and such bodies interposed between the plates as separators.
There are already methods of fixing the sulfuric acid electrolyte of a lead-acid battery of this kind wherein the electrolyte is absorbed and retained in porous bodies as separators (refer, for example, to U.S. Pat. No. 3,862,861 to D. H. McClelland et al. and U.S. Pat. No. 3,553,020 to R. L. Corbin et al.) and wherein the electrolyte is gelled and fixed (refer, for example, to U.S. Pat. No. 3,765,942 to U. Jache and U.S. Pat. No. 3,776,779 to B. L. Johnson). The best porous body to be used in the former method is a porous body formed mostly of glass fibers of a diameter not thicker than 1.0 micron. If it is used, a battery particularly very high in discharge performance, life performance and gas recombination performance will be obtained. However, with it, there are defects that, as special glass fibers are used, the cost is high, that, in order to improve the leakproofness, it is necessary to strictly keep the poured amount of the sulfuric acid electrolyte the same as or rather smaller than the total pore volume of the plate group and that, even in the control of this electrolyte pouring step, the cost in high. Further, in this kind of lead-acid battery, there are drawbacks: the capacity is regulated usually by the amount of the electrolyte instead of the positive and negative plates or, in other words, by the amount of the sulfuric acid, on the other hand, the amount of the electrolyte is strictly limited from the viewpoint of the gas recombination and leakproofness, therefore, if the capacity of the battery is to be increased within the limited volume, the amount of the sulfuric acid radical must be increased by using a sulfuric acid electrolyte of a high concentration, therefore the self-discharge will increase, the deterioration of the plates will be accelerated and the life performance will be reduced. On the other hand, in the latter method, there are the drawbacks that, as the gelling agent of a high concentration is used, the internal resistance will become high and the discharge characteristic, and particularly the high rate discharge characteristic, will be very bad. Further, when the sulfuric acid electrolyte is gelled, plasmolysis water will be always produced within the battery. Therefore, there is a defect that the leakproofness of the battery is essentially lower than in using the above-described porous bodies. Further, as the gelled sulfuric acid electrolyte is used, it is so difficult to pour the electrolyte into the battery that the electrolyte pouring step will become complicated and the obtained battery cannot help but be expensive.
An object of the present invention is to provide a sealed lead-acid battery which is high in its discharge characteristic and particularly in its high rate discharge characteristic, has no leakage of the electrolyte and has a long service life.
Another object of the present invention is to provide a process for cheaply and simply producing the above-described battery.